Umbrello UML Modeller is a Scripts software developed by Jonathan Riddell. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Umbrello UML Modeller:

BSEditor: Umbrello UML Modeller is a Unified Modelling Language diagram tool for KDE. It is able to produce Class Diagrams, Sequence diagrams, Collaboration diagrams, Use Case diagrams, Activity diagrams, and State diagrams. It uses an XMI-based file format. It is Now part of KDE and will be released with KDE 3.2